1. Field of the Invention
The present invention relates to a field emission device and a method for manufacturing of the field emission device, and also relates to a field emission display device including the field emission device.
2. Description of the Related Arts
These days, a flat type (flat panel type) display device has been studied as an image display device by which a cathode-ray tube (CRT) is replaced. As such flat type display device, a liquid crystal display device (LCD), an electroluminescence display device (ELD), and a plasma display device (PDP) can be given. In addition, a display device that utilizes an electron emitted due to electric field effect to emit light with electron beam exciting, a so-called field emission display device (FED: field emission display, is suggested to which attention is paid from the view point of a high performance for displaying a moving image.
The FED has a first substrate with a cathode electrode and a second substrate with an anode electrode to which a phosphor layer is put, which are arranged to face each other and are bonded with a sealing member, and the space enclosed by the first and second substrates and the sealing member is kept high vacuum. An electron emitted from the cathode electrode is moved through the enclosed space to excite the phosphor layer put to the anode electrode, and then light is emitted to obtain an image display.
The FED can be classified in a diode-type, a triode-type, or a tetrode-type by electrode. In the case of a diode-type FED, a stripe-shaped cathode electrode is formed on a surface of a first substrate and a stripe-shaped anode electrode is formed on a surface of a second substrate, and the cathode electrode is orthogonal to the anode electrode at a distance from several μm to several mm. At the intersection of the cathode electrode and the anode electrode through vacuum, voltage up to 10 kV is applied to emit an electron between the cathode electrode and the anode electrode. The electron is made to get to a phosphor layer put to the anode electrode to excite the phosphor, and then light is emitted to display an image.
In the case of a triode-type FED, over a cathode electrode formed on a first substrate, a gate electrode that is orthogonal to the cathode electrode is formed through an insulating film. The cathode electrodes and the gate electrode have a stripe shape or a matrix shape, and an electron emission portion (electron emitter) as an electron source is formed at the intersecting portion thereof through the insulating film. An electron is emitted from the electron emission portion by applying voltage to each of the cathode electrode and the gate electrode. The electron is attracted to an anode electrode of a second substrate, to which higher voltage is applied than to the gate electrode, to excite a phosphor layer put to the anode electrode, and then light is emitted to display an image.
In the case of a tetrode-type FED, a plate-shaped or filmy convergence electrode, which has an opening portion with respect to each dot, is formed between a gate electrode and an anode electrode of a triode-type FED. With the convergence electrode provided, an electron emitted from an electron emission portion is converged with respect to each dot to excite a phosphor layer put to an anode electrode, and then light is emitted to display an image.
A field emission device has an electron emission portion that emits an electron, which is formed on a cathode electrode. The field emission device may have a gate electrode over the cathode electrode through an insulating film. Now, as the field emission device of a field emission display device, various structures are proposed. Specifically, there are a spint-type field emission device, a surface-type field emission device, an edge-type field emission device, and MIM (Metal-Insulator-Metal).
The spint-type field emission device is a field emission device that has a conical electron emission portion formed on a cathode electrode. It is possible to give such advantages that 1) the electron drawing efficiency is high since the electron emission portion is arranged in the vicinity of the center of the gate electrode, where the electric field is most concentrated, 2) it is possible to draw a pattern of an arrangement of the field emission device with accuracy to make it easy to optimize an arrangement of distribution of electric field, and in-plane uniformity of drawn current is high 3) the directivity of electron emission is regular, compared to the other field emission device.
As conventional spint-type field emission device, there are a conical field emission device formed by evaporation of metal (page 11 and FIGS. 9A to 10 C of Japanese Patent Laid-Open 2002-175764) and a conical field emission device formed with the use of MOSFET (page 3 to 4 and FIG. 1 of Japanese Patent Laid-Open Hei 11-102637).
A manufacturing process of the field emission device disclosed in Japanese Patent Laid-Open 2002-175764 will be shown with reference to FIGS. 28A to 28D. As shown in FIG. 28A, an interlayer insulating film 1103 and a gate electrode 1104 are formed on a stripe-shaped cathode electrode 1102 formed on a glass substrate 1101.
Next, as shown in FIG. 28B, the gate electrode 1104 and the interlayer insulating film 1103 are etched to form an opening portion 1105. Then, oblique evaporation of aluminum is performed with respect to the gate electrode to form a peeling layer 1106 protruding from an open end of the gate electrode in an appentice shape.
Next, as shown in FIG. 28C, evaporation of metal such as molybdenum is performed vertically to the whole substrate. Since a metal layer 1107 is deposited on the appentice-shaped peeling layer 1106 and the opening portion 1105 become reduced in size, metal to be deposited on a basal plane of the opening portion 1105, that is, on the cathode electrode 1102, is gradually limited to metal passing in the vicinity of the center of the opening portion 1105. Hereby, a conical deposit 1108 is formed on the basal plane to become an electron emission portion.
Next, as shown in FIG. 28D, wet etching to the interlayer insulating film 1103 below the gate electrode 1104 is performed to form a shape 1109 of the gate electrode protruding from an upper portion of the interlayer insulating layer.
However, it is difficult to form an appentice-shaped peeling layer in a uniform size by oblique evaporation, some kind of in-plane variation or lot-to-lot variation is unavoidable. In addition, there are also problems that a large-sized evaporation system is needed, throughput is lowered, the residue in removing a peeling layer formed on a large area causes contamination of a cathode electrode or a field emission device to lower yield of manufacturing a display device.
On the other hand, the field emission device disclosed in Japanese Patent Laid-Open Hei 11-102637 uses MOSFET, and a semiconductor substrate is used. Therefore, the size of the substrate is limited, and there is a problem that mass production is difficult to lower throughput.